406 CHOLERA 



gradually dimmish in number, and ultimately disappear. It 

 must not, however, be inferred from such experiments that a 

 similar result will necessarily follow in nature, as any particular 

 saprophytic organism requires a special habitat that is, certain 

 suitable conditions for its growth in competition with other 

 organisms. Though we can state generally that the conditions 

 favourable for the growth of the cholera spirillum are a warm 

 temperature, moisture, a good supply of oxygen, and a consider- 

 able proportion of organic material, we do not know the exact 

 circumstances under which it can nourish for an indefinite period 

 of time as a saprophyte. The fact that the area in which 

 cholera is an endemic disease is so restricted tends to show that 

 the conditions for a prolonged growth of the spirillum outside 

 the body are not usually supplied. Yet, on the other hand, 

 there is no doubt that in ordinary conditions it can live a 

 sufficient time outside the body and multiply to a sufficient 

 extent, to explain all the facts known with regard to the per- 

 sistence and spread of cholera epidemics. 



Numerous experiments show that the cholera organisms are, 

 as a rule, rapidly killed by drying, usually in two or three 

 minutes when the drying has been thorough, and it is inferred 

 from this that they cannot be carried in the living condition for 

 any great distance through the air, a conclusion which is well 

 supported by observations on the spread, of the disease. Cholera 

 is practically always transmitted by means of water or food 

 contaminated by the organism, and there is no doubt that con- 

 tamination of the water supply by choleraic discharges is the 

 chief means by which areas of population are rapidly infected. 

 It has been shown that if flies are fed on material containing 

 cholera organisms, the organisms may be found alive within their 

 bodies twenty -four hours afterwards. And further, Haffkine 

 found that sterilised milk might become contaminated with 

 cholera organisms, if kept in open jars to which flies had free 

 access, in a locality infected by cholera. It is quite possible 

 that infection may be carried by this agency in some cases. 



Experimental Inoculation. In considering the effects of 

 inoculation with the cholera organism, we are met with the 

 difficulty that none of the lower animals, so far as is known, 

 suffer from the disease under natural conditions. Even in places 

 where cholera is endemic, no corresponding affection has been 

 observed in any animals. And further, before the discovery of 

 the cholera organism, various efforts had been made to induce 

 the disease in animals by feeding them with cholera dejecta, but 

 without success. It is therefore not surprising that the earlier 



